1. Field of the Invention
This invention is in the field of Synthetic Aperture Radar (SAR) imaging using a plurality of receive channels of a segmented antenna to identify and compensate for ambiguities in wide coverage SAR images.
2. Description of the Related Art
Synthetic Aperture Radar (SAR) radar is used for ground mapping as well as target identification. The general principle behind SAR is to coherently combine the amplitude and phase information of radar returns from a plurality of sequentially transmitted pulses from a relatively small antenna on a moving platform.
The plurality of returns creating a SAR image generated by the transmitted pulses along a known path of the platform make up a frame length. During the frame length, amplitude as well as phase information returned from each of the pulses, for each of many range bins, is preserved. The SAR image is formed from the coherent combination of the amplitude and phase of return(s) within each range bin, motion compensated for spatial displacement of the moving platform during the acquisition of the returns for the duration of the frame length.
The plurality of pulses transmitted during an SAR frame length, when coherently combined and processed, result in image quality comparable to a longer antenna, corresponding approximately to the “length” traveled by the antenna during the frame length.
Range target resolution in SAR images is determined by the radar bandwidth. Range resolution is inversely proportional to radar bandwidth. That is, the higher the bandwidth, the smaller the details of a radar scatterer can be discerned in a range bin. Therefore, ideally, radar imaging is best enhanced by short pulses of high peak power.
It is desirable to produce a SAR image covering as much of an area as possible in one frame length. Unfortunately, both for spotlight and side looking, swath SAR modes, there is an inherent constraint in the size of the area that can be acquired in one frame length. If the frame is too long in the range direction, or too wide in the cross range direction, or both, ambiguities will arise in the imaging process. That is, because of the processing involved, certain scatterers will appear in more than one location in the final SAR image. This ghost like superposition on the real image tends to degrade the actual image, affecting its clarity thereby limiting its utility.